1. Field of the Invention
The invention relates to metallurgy and, more particularly, to a method for treating items from magnetically soft alloys.
The present invention can find a most effective application in manufacture of parts of radio-electronic, relay and switching apparatus of optical-and-mechanical and automation systems.
In addition, the present invention can be employed for manufacturing parts from magnetically soft alloys for computer, aircraft and space equipment.
2. Description of the Prior Art
Present-day instrument manufacture imposes strict requirements for physico-chemical properties of parts of magnetic systems from magnetically soft alloys. Thus, magnetically soft alloys are required to have high and stable magnetic properties along with a high electric resistivity; a high corrosion resistance in moist atmospheres, in marine climates, in industrial atmospheres in acid solutions and in fungous media and; in some applications, both high hardness of the surface and wearability thereof.
The existing magnetically soft alloys fail to meet the above set of conditions, thus lowering the reliability and durability of electromagnetic instruments and devices.
Such a variety of physico-chemical properties cannot be obtained by integral alloying, as acquisition of some properties is accompanied by a loss of others. Neither can this problem be solved by other currently available processing means, such as vacuum annealing (or annealing in an atmosphere of hydrogen, argon or dissociated ammonia) with subsequent application of chemical coats, galvanizing and electroplating of items from alloys based on iron, nickel and cobalt; nor by vacuum annealing or vacuum annealing with subsequent thermal oxidizing of items from iron-silicon and iron-nickel alloys.
The above kinds of annealing affect only the structurally sensitive magnetic properties (magnetic permeability, coercive force) and fail to provide the necessary set of physico-chemical properties, since, for example, annealing lowers resistance of parts to corrosion and their wearability.
Vacuum annealing with subsequent thermal oxidizing is effective with respect only to parts made of thin and extra thin rolled alloy products which can be provided with a protective oxide film inhibiting their further oxidation (for example, when processing parts of iron-silicon and iron-nickel alloys). Galvanizing, chemical coating and electrochemical plating employed subsequently to one of the kinds of annealing with a view to improving the corrosion and the wear resistance of parts fail in some instances to provide coats of required resistance to corrosion and wear, the coats possessing a poor continuity of deposited layers and poor adhesion strength, whereas high residual stresses in the coats cause their cracking and peeling in service. In addition, the above coats lower the structurally sensitive magnetic characteristics, stability of properties and substantially increase manufacturing cycle.
There is known a method for diffusion chromizing of structural steels and alloys, employed with a view to enhancing wearability and corrosion resistances, consisting in heating items in a powder mixture of chromium, aluminum oxide and ammonia, exposing the items to temperatures between 800.degree. and 1200.degree. C. for over an hour, followed by subsequent cooling thereof.
However, the known method for diffusion chromizing fails to improve the magnetic properties of magnetically soft alloys and stability thereof, since a necessary set of physico-chemical properties in parts from magnetically soft alloys is possible only at appropriate rates of heating and cooling, which are not provided for by the existing methods of diffusion chromizing.
There is known a method for diffusion chromizing of parts from permalloy, heated to 800.degree. C. and above in an atmosphere of a chromium halide compound and gaseous hydrogen with subsequent cooling of items (Japan, patent application no. 45-123347, filed 31.XII.70).
However, notwithstanding, intricate processing requiring complicate and costly equipment, the above method fails to provide the necessary set of physico-chemical properties. For example, the method cannot provide a necessary wearability of parts subject to intensive deterioration, since it necessarily involves the use of a gaseous hydrogen atmosphere where items decarburize readily. This produces a solid solution of chromium in iron in the surface layers of the items, the wearability of which is rather poor. In addition, this method fails to ensure high corrosion resistance in chlorine ion media, as the thickness of the diffusion layer is small.